Oestrogens and calcium regulatory hormones: potential implications for bone.

Postmenopausal oestrogen deficiency is associated with the development of osteoporosis. Oestrogen therapy prevents further bone loss but does not have an anabolic effect. The only treatment with an anabolic effect on bone is intermittent parathyroid hormone treatment. Oestrogens have a direct action on the parathyroid to increase parathyroid hormone gene expression and parathyroid hormone secretion. They exert this effect at doses that are too low to cause the uterotrophic effect of oestradiol. Osteoporotic patients have a decreased parathyroid hormone secretory response to changes in serum calcium, supporting the experimental data that oestrogens have a direct effect on the parathyroid. The value of parathyroid hormone treatment is limited by the need for parenteral therapy. The ability of oestrogens to increase parathyroid hormone secretion suggests that the intermittent administration of oestrogen analogues, at doses that exert no effects on breast tissue and the uterus, would be the optimal treatment for osteoporosis.